The present invention relates to a transaction processing system in which a central unit is connected to terminal units through communication lines or signal lines so that communication of data is established for carrying out the transaction process.
It has been practiced for the automatic cash dispenser (CD) and the like in the bank service system that when a customer opens an account with a bank, the bank issues a magnetic card with a secret code specified by the customer and an account number recorded thereon in order to provide an identification of the legitimate user who is making a transaction using the cash dispenser. When the customer deals with the cash dispenser, he (she) is requested to enter the magnetic card and also key the secret code into the cash dispenser, and entry of transaction data is allowed only if the secret code recorded on the magnetic card coincides with the secret code keyed-in by the user. There have been practiced various means of preventing an illegal transaction by checking the legitimacy of user through use of the secret code, such as seen in the illegal transaction preventing system for checking that the user of the cash dispenser is a legitimate user who knows the secret code recorded on the magnetic card.
As described above, the conventional method of preventing an illegal transaction which has been commonly practiced is that of using an installation type equipment, such as a cash dispenser, in which it is checked whether the transacting operator is an eligible person who knows the specific key word, thereby preventing an illegal transaction.
However, in the case of a transportable terminal unit, which is carried by the canvasser of the bank to the customer for making a transaction and which is connected to the central unit for data transmission using a customer's telephone set, the unit could be stolen for purposes of effecting an illegal transaction or an illegal transaction could be carried out using a device which cannot be used in its own system (e.g., the central unit of bank A which carries out the transaction by connecting only the transportable terminal device owned by bank A is connected with a transportable terminal unit owned by bank B, or a device having the same function as that of the transportable terminal unit owned by bank A is illegally manufactured using a microcomputer and connected to the central unit of bank A). Therefore, the transaction system using transportable terminal units which are connected to the central unit through public communication lines cannot be prevented from illegal actions only by checking the legitimacy of the unit operator using a secret code and the like as has been described in the case of an illegal transaction preventing system for a cash dispenser.